Yes, you can with pruning shears or something similar. But it doesn't give such a nice cut and you only have 2 end pieces. This means that the gliders could fall out, depending on the situation.
I found a connecting piece in the Gardinia products that actually does not belong to the Flexline product line, but to the Perfectline line. I was able to connect 2 Flexline rails of 350m each with this. I ordered this from Jemoli at the time. But I can no longer find it there. At Gardinia.de it can be found under Perfectline accessories, article number: 32486.